The spool can be a long, thin "pipe" of wound cable that goes with one end of the "pipe" pointing to the rear (up). You can put an arbitrary amount of cable in a given hole diameter by making the spool taller.
(Google image search suggests that a similar approach has been taken by the TOW, it's not a spool that could be reversed by adding a motor to an axis, more like a tightly packed coil that gets straightened as wire is pulled out)
As for the energy, I assumed GP was thinking of solar panels on the surface. I also assume that we share scepticism based on the low sun intensity out in the orbit of Jupiter... (and that's before you even start wondering how much further away from the melting point that ice will be than all ice of conventional human experience)
>You can put an arbitrary amount of cable in a given hole diameter by making the spool taller.
Wouldn't this be limited to the tensile strength of the material and the weight of the cable? Granted, Europa has much less gravity, but 25km is a lot of cable weight.
Consider something as small as fishing line; one online estimate gives it .245g/m. At 25km, that's over 3 tons of line weight hanging down a hole on Earth or nearly 800 lbs on Europa.
I think there are still mechanics at play that would have to be considered.
>The probe bears on the ice below it
This implies it is bearing the weight of the entire cable above it. So instead of the tensile stress being the limiting factor, it's not the compressive stress. If you're intent is to retract the spool, it would still be in tensile stress as it comes up. (And you'd need enough torque to do so. But maybe you the plan would be to abandon in place).
>What you have to worry about is the ice shifting and severing the cable.
Could you embed a series of metallic needles as you melted your way down, then communicate via radio waves that travel needle to needle? They would not need to be connected. Just close by.
(Google image search suggests that a similar approach has been taken by the TOW, it's not a spool that could be reversed by adding a motor to an axis, more like a tightly packed coil that gets straightened as wire is pulled out)
As for the energy, I assumed GP was thinking of solar panels on the surface. I also assume that we share scepticism based on the low sun intensity out in the orbit of Jupiter... (and that's before you even start wondering how much further away from the melting point that ice will be than all ice of conventional human experience)